When heresy is used today with reference to Christianity, it denotes the formal denial or doubt of a core doctrine of the Christian faith[1] as defined by one or more of the Christian churches.[2] It should be distinguished from both apostasy and schism,[2] apostasy being nearly always total abandonment of the Christian faith after it has been freely accepted,[3] and schism being a formal and deliberate breach of Christian unity and an offence against charity without being based essentially on doctrine.[4]

The Catholic Church distinguishes between "formal heresy" and "material heresy". The former involves willful and persistent adherence to an error in matters of faith and is a grave sin for which the church applies the penalty of excommunication.[2] "Material heresy" is the holding of erroneous opinions through no fault of one's own and is not sinful. Protestants can fall into either the first or the second group, depending on whether they are in invincible ignorance[3] while the Eastern Orthodox are considered to be schismatic but are recognised as local churches, but "defective" (according to Dominus Iesus) and severed from the Catholic Church,[5] which in Catholic teaching is the "only true Church".

Historical examination of heresies focuses on a mixture of theological, spiritual, and socio-political underpinnings to explain and describe their development. For example, accusations of heresy have been levelled against a group of believers when their beliefs challenged, or were seen to challenge, Church authority. Some heresies have also been doctrinally based, in which a teaching was deemed to be inconsistent with the fundamental tenets of orthodox dogma.

The study of heresy requires an understanding of the development of orthodoxy and the role of creeds in the definition of orthodox beliefs. Orthodoxy has been in the process of self-definition for centuries, defining itself in terms of its faith and changing or clarifying beliefs in opposition to people or doctrines that are perceived as incorrect. The reaction of the orthodox to heresy has also varied over the course of time; many factors, particularly the institutional, judicial, and doctrinal development of the Church, have shaped this reaction.[citation needed] Heresy remained an officially punishable offence in Roman Catholic nations until the late 18th century. In Spain, heretics were prosecuted and punished during the Counter-Enlightenment movement of the restoration of the monarchy there after the Napoleonic Era.[citation needed]

The word heresy comes from haeresis, a Latin transliteration of the Greek word originally meaning choosing, choice, course of action, or in an extended sense school of thought[6] then eventually came to denote warring factions and the party spirit by the first century. The word appears in the New Testament and was appropriated by the Church to mean a sect or division that threatened the unity of Christians. Heresy eventually became regarded as a departure from orthodoxy, a sense in which heterodoxy was already in Christian use soon after the year 100.[7]

In the fifth century, a formal distinction between anathema and excommunication evolved, where excommunication entailed cutting off a person or group from the rite of Eucharist and attendance at worship, while anathema meant a complete separation of the subject from the Church.

The development of doctrine, the position of orthodoxy, and the relationship between the various opinions is a matter of continuing theological debate. Since most Christians today subscribe to the doctrines established by the Nicene Creed, modern Christian theologians tend to regard the early debates as a unified orthodox position (see also Proto-orthodox Christianity and Paleo-orthodoxy) against a minority of heretics. Other scholars, drawing upon, among other things, distinctions between Jewish Christians, Pauline Christians, and other groups such as Gnostics and Marcionites, argue that early Christianity was fragmented, with contemporaneous competing orthodoxies.[9]

Early attacks upon alleged heresies formed the matter of Tertullian's Prescription Against Heretics (in 44 chapters, written from Rome), and of Irenaeus' Against Heresies (ca 180, in five volumes), written in Lyon after his return from a visit to Rome. The letters of Ignatius of Antioch and Polycarp of Smyrna to various churches warned against false teachers, and the Epistle of Barnabas accepted by many Christians as part of Scripture in the 2nd century, warned about mixing Judaism with Christianity, as did other writers, leading to decisions reached in the first ecumenical council, which was convoked by the Emperor Constantine at Nicaea in 325, in response to further disruptive polemical controversy within the Christian community, in that case Arianist disputes over the nature of the Trinity.

The development of doctrine, the position of orthodoxy, and the relationship between the early Church and early heretical groups is a matter of academic debate. Walter Bauer proposed a thesis that in earliest Christianity, orthodoxy and heresy do not stand in relation to one another as primary to secondary, but in many regions heresy is the original manifestation of Christianity. Scholars such as Pagels and Ehrman have built on Bauer's original thesis. Drawing upon distinctions between Jewish Christians, Gentile Christians, and other groups such as Gnostics, they see early Christianity as fragmented and with contemporaneous competing orthodoxies.[10] Ehrman's view is that while the specifics of Bauer's demonstration were later rejected, his intuitions are broadly accepted by scholars and got confirmed beyond what Bauer might have guessed.[11]

The Pattern of Christian Truth: A Study in the Relations between Orthodoxy and Heresy in the Early Church, written by H. E. W. Turner, is one of many scholarly responses to the concept of early Christian origins as being ambiguous. Turner's response was in objection to Bauer's. In 2006, Darrell Bock[12] addressed Walter Bauer's theory, stating that it does not show an equality between the established church and outsiders including Simon Magus. In The Cambridge History of Christianity Volume 1,[13]Origins to Constantine, Walter Bauer's hypothesis was addressed again; this time in the introduction of the book it states each article addressed the uniqueness of each early Christian community but stated that the tenets of the mainstream or Catholic Church insured that each early Christian community did not remain isolated. The Russian philosopher Aleksey Khomyakov stated that the very church was the idea of submission and compromise of the individual to God through the idea of catholic or the Russian equivalent sobornost. Russian Orthodox theologian Father Georges Florovsky addressed the concept of sobornost as the concept of Orthodox Christianity after rejecting the World Church Council as being Catholic or orthodox simply because it expressed unity in Christ. Florovksy stating as an apology that the very tenet of Catholic or sobornost was the original church's response (through the patristic works of the early fathers) to the idea that there were multiple orthodoxies and no real heresies.

Before AD 313, the "heretical" nature of some beliefs was a matter of much debate within the churches, and there was no true mechanism in place to resolve the various differences of beliefs. Heresy was to be approached by the leader of the church according to Eusebius, author of The Church History. It was only after the legalisation of Christianity, which began under Constantine I in AD 313 that the various beliefs of the Church began to be made uniform and formulated as dogma through the canons promulgated by the General Councils. Each phrase in the Nicene Creed, which was hammered out at the Council of Nicaea, addresses some aspect that had been under passionate discussion prior to Constantine I, and closes the books on the argument, with the weight of the agreement of the over 300 bishops, as well as Constantine I in attendance. [Constantine had invited all 1800 bishops of the Christian church (about 1000 in the east and 800 in the west). The number of participating bishops cannot be accurately stated; Socrates Scholasticus and Epiphanius of Salamis counted 318; Eusebius of Caesarea, only 250.] In spite of the agreement reached at the council of AD 325, the Arians, who had been defeated, dominated most of the church for the greater part of the 4th century, often with the aid of Roman emperors who favoured them.

Irenaeus (c. 130 – c. 202) was the first to argue that his "orthodox" position was the same faith that Jesus gave to the apostles, and that the identity of the apostles, their successors, and the teachings of the same were all well-known public knowledge. This was therefore an early argument supported by apostolic succession. Irenaeus first established the doctrine of four gospels and no more, with the synoptic gospels interpreted in the light of John. Irenaeus' opponents, however, claimed to have received secret teachings from Jesus via other apostles which were not publicly known. Gnosticism is predicated on the existence of such hidden knowledge, but brief references to private teachings of Jesus have also survived in the canonic Scripture as did warning by the Christ that there would be false prophets or false teachers. Irenaeus' opponents also claimed that the wellsprings of divine inspiration were not dried up, which is the doctrine of continuing revelation.

The first known usage of the term 'heresy' in a civil legal context was in 380 by the "Edict of Thessalonica" of Theodosius I. Prior to the issuance of this edict, the Church had no state-sponsored support for any particular legal mechanism to counter what it perceived as 'heresy'. By this edict, in some senses, the line between the Catholic Church's spiritual authority and the Roman State's jurisdiction was blurred. One of the outcomes of this blurring of Church and State was a sharing of State powers of legal enforcement between Church and State authorities, with the state enforcing what it determined to be orthodox teaching.

Within five years of the official 'criminalization' of heresy by the emperor, the first Christian heretic, Priscillian, was executed in 385 by Roman officials. For some years after the Protestant Reformation, Protestant denominations were also known to execute those whom they considered heretics.

The earliest controversies were generally Christological in nature; that is, they were related to Jesus' (eternal) divinity or humanity. The orthodox teaching, as it developed, is that Christ was fully divine and at the same time fully human, and that the three persons of the Trinity are co-equal and co-eternal.

This position was challenged in the 4th century by Arius. Arianism held that Jesus, while not merely mortal, was not eternally divine and was, therefore, of lesser status than God the Father (John 14:28). Trinitarianism held that God the Father, God the Son, and the Holy Spirit were all strictly one being with three hypostases. Many groups held dualistic beliefs, maintaining that reality was composed into two radically opposing parts: matter, usually seen as evil, and spirit, seen as good. Docetism held that Jesus' humanity was merely an illusion, thus denying the incarnation. Others held that both the material and spiritual worlds were created by God and were therefore both good, and that this was represented in the unified divine and human natures of Christ.[14]

Urgent concerns with the uniformity of belief and practice have characterized Christianity from the outset. In the three centuries between the crucifixion and the First Council of Nicaea in 325, the religion was at times an illegal, underground movement spreading within the urban centres of the Roman Empire, a process bolstered through merchants and travel through the empire. The process of establishing orthodox Christianity was set in motion by a succession of different interpretations of the teachings of Christ being taught after the crucifixion, though Christ himself is noted to have spoken out against false prophets and false christs within the Gospels themselves: Mark 13:22 (some will arise and distort the truth in order to draw away disciples), Matthew 7:5-20, Matthew 24:4, Matthew 24:11 Matthew 24:24 (For false christs and false prophets will arise). On many occasions in Paul's epistles, he defends his own apostleship, and urges Christians in various places to beware of false teachers, or of anything contrary to what was handed to them by him. The epistles of John and Jude also warn of false teachers and prophets, as does the writer of the Book of Revelation and 1 John. 4:1, as did the Apostle Peter warn in 2 Peter. 2:1-3. Due to this, in the first centuries of Christianity, churches had locally begun to make a statement of faith in line with mainstream Christian doctrine a prerequisite for baptism. The reason for this demand was to insure that new converts would not be followers of teachings that conflicted with widely accepted views of Christianity such as Gnosticism and other movements that later were considered heretical by church leaders. These statements of faith became the framework for ecumenical creeds such as the Apostles Creed and the Nicene Creed. It was against these creeds that teachings were judged in order to determine orthodoxy and to establish teachings as heretical. The first ecumenical and comprehensive statement of belief, the Nicene Creed, was formulated in 325 at the First Council of Nicaea.

The edict of Theodosius II (435) provided severe punishments for those who had or spread writings of Nestorius.[15] Those who possessed writings of Arius were sentenced to death.[16]

The Second Ecumenical Council was held at Constantinople in 381, presided over by the Patriarchs of Alexandria and Antioch, with 150 bishops, defining the nature of the Holy Spirit against those asserting His inequality with the other persons of the Trinity.

The Third Ecumenical Council is that of Ephesus, a stronghold of Cyrillian Christianity, in 431. It was presided over by the Patriarch of Alexandria, with 250 bishops and was mired in controversy because of the absences of the Patriarchs of Constantinople, and Antioch, the absence of the Syrian Clergy, and violence directed against Nestorius, and his supporters. It affirmed that Mary is the "Bearer" of God (Theotokos), contrary to the teachings of Nestorius, and it anathematized Nestorius. A mirror Council held by Nestorius, the Patriarch of Antioch and the Syrian clergy affirmed Mary as Christokos, "Bearer" of Christ, and anathematized Cyril of Alexandria.

The Fourth Ecumenical Council is that of Chalcedon in 451, Patriarch of Constantinople presiding, 500 bishops, affirmed that Jesus is truly God and truly man, without mixture of the two natures, contrary to Monophysite teaching.

The Fifth Ecumenical Council is the second of Constantinople in 553, interpreting the decrees of Chalcedon and further explaining the relationship of the two natures of Jesus; it also condemned the teachings of Origen on the pre-existence of the soul, etc.

The Sixth Ecumenical Council is the third of Constantinople in 681; it declared that Christ has two wills of his two natures, human and divine, contrary to the teachings of the Monothelites.

From the late 11th century onward, heresy once again came to be a concern for Catholic authorities, as reports became increasingly common. The reasons for this are still not fully understood, but the causes for this new period of heresy include popular response to the 11th-century clerical reform movement, greater lay familiarity with the Bible, exclusion of lay people from sacramental activity, and more rigorous definition and supervision of Catholic dogma. The question of how heresy should be suppressed was not resolved, and there was initially substantial clerical resistance to the use of physical force by secular authorities to correct spiritual deviance. As heresy was viewed with increasing concern by the papacy, however, the "secular arm" was used more frequently and freely during the 12th century and afterward.

In later years, the Church instituted the Inquisition, an official body charged with the suppression of heresy. This began as an extension and more rigorous enforcement of pre-existing episcopal powers (possessed, but little used, by bishops in the early Middle Ages) to inquire about and suppress heresy, but later became the domain of selected Dominicans and Franciscans[17] under the direct power of the Pope. The use of torture to extract confessions was authorized by Innocent IV in 1252.[18] The Inquisition was active in several nations of Europe, particularly where it had fervent support from the civil authority. The Albigensian Crusade (1209–1229) was part of the Catholic Church's efforts to crush the Cathars. It is linked to the movement now known as the Medieval Inquisition. The Spanish Inquisition was particularly brutal in its methods, which included the burning at the stake of many heretics. However, it was initiated and substantially controlled by King Ferdinand of Spain rather than the Church; King Ferdinand used political leverage to obtain the Church's tacit approval.[citation needed] Another example of a medieval heretic movement is the Hussite movement in the Czech lands in the early 15th century. The last person to be burned alive at the stake on orders from Rome was Giordano Bruno, executed in 1600 for a collection of heretical beliefs including Copernicanism, belief of an unlimited universe with innumerable inhabited worlds, opinions contrary to the Catholic faith about the Trinity, divinity of Christ, and Incarnation.

Tondrakians - an Armenian group (9th to 11th centuries) who advocated the abolition of the Church along with all its traditional rites.

Bogomils – a group arising in the 11th century in Macedonia and the Balkans who sought a return to the spirituality of the early Christians and opposed established forms of government and church.

Gundolfo – an itinerant 11th century preacher near Lille, France, who taught that salvation was achieved through a virtuous life of abandoning the world, restraining the appetites of the flesh, earning food by the labor of hands, doing no injury to anyone, and extending charity to everyone of their own faith.

Cathars – a major Christian movement in the Languedoc region of southern France from the 11th to 13th centuries. The Cathars believed that human souls were the spirits of angels trapped within the physical creation of an evil god. Through living a pure and sinless life, the soul could become perfect and free from the snare of matter.

Apostolic Brethren (later known as Dulcinians) – a 13th to 14th century sect from northern Italy founded by Gerard Segarelli and continued by Fra Dolcino of Novara. The Apostolic Brethren rejected the worldliness of the church and sought a life of perfect sanctity, in complete poverty, with no fixed domicile, no care for the morrow, and no vows.

Fraticelli (or Spiritual Franciscans) – Franciscan extremists through the 13th to 15th centuries who regarded the wealth of the Church as scandalous.

Nicholas of Basel – a 14th century Swiss leader who, after a spiritual experience, taught that he had the authority to use episcopal and priestly powers (even though he was not ordained), that submission to his direction was necessary for attaining spiritual perfection, and that his followers could not sin even though they committed crimes or disobeyed both the Church and pope.

The last case of an execution by the inquisition was that of the schoolmaster Cayetano Ripoll, accused of deism by the waning Spanish Inquisition and hanged on 26 July 1826 in Valencia after a two-year trial.[19] Eight years later in 1834, Spain, the last remaining government to still be providing the Catholic Church with the right to pronounce and effect capital punishment, formally withdrew that right from the Church. The era of such absolute Church authority had lasted some 1,449 years, from AD 385 through to 1834. The number of people executed as heretics as sentenced by various church authorities is not known; however it most certainly numbers into the several thousands. Coincidentally, the first heretic executed had been a Spaniard, Priscillian; the most notorious organization known for the persecution of heretics had been based in Spain, the Spanish Inquisition, and the last heretic executed had been a Spaniard, Cayetano Ripoll. Thus, the era of the execution of heretics by the Catholic Church had come to an end.

Well into the 20th century, Catholics defined Protestants as heretics. Thus, Hilaire Belloc, in his time one of the most conspicuous speakers for Catholicism in Britain, was outspoken about the "Protestant heresy". He even defined Islam as being "a Christian heresy", on the grounds that Muslims accept many of the tenets of Christianity but deny the divinity of Christ.

However, in the second half of the century, and especially in the wake of the Second Vatican Council, the Catholic Church, in the spirit of ecumenism, tended to diminish the effects of Protestantism as a formal heresy by referring to many Protestants who, as material heretics, "through no fault of their own do not know Christ and his Church",[20] even though the teachings of Protestantism are indeed formally heretical from a Catholic perspective. Modern usage in ecumenical contexts favors referring to Protestants as "separated brethren". In his book The Meaning of Christian Brotherhood, Pope Benedict XVI wrote that:

The difficulty in the way of giving an answer is a profound one. Ultimately it is due to the fact that there is no appropriate category in Catholic thought for the phenomenon of Protestantism today (one could say the same of the relationship to the separated churches of the East). It is obvious that the old category of ‘heresy’ is no longer of any value. Heresy, for Scripture and the early Church, includes the idea of a personal decision against the unity of the Church, and heresy’s characteristic is pertinacia, the obstinacy of him who persists in his own private way. This, however, cannot be regarded as an appropriate description of the spiritual situation of the Protestant Christian. In the course of a now centuries-old history, Protestantism has made an important contribution to the realization of Christian faith, fulfilling a positive function in the development of the Christian message and, above all, often giving rise to a sincere and profound faith in the individual non-Catholic Christian, whose separation from the Catholic affirmation has nothing to do with the pertinacia characteristic of heresy. Perhaps we may here invert a saying of St. Augustine’s: that an old schism becomes a heresy. The very passage of time alters the character of a division, so that an old division is something essentially different from a new one. Something that was once rightly condemned as heresy cannot later simply become true, but it can gradually develop its own positive ecclesial nature, with which the individual is presented as his church and in which he lives as a believer, not as a heretic. This organization of one group, however, ultimately has an effect on the whole. The conclusion is inescapable, then: Protestantism today is something different from heresy in the traditional sense, a phenomenon whose true theological place has not yet been determined.[21]

Some of the doctrines of Protestantism that the Catholic Church considers heretical are the belief that the Bible is the only source and rule of faith (sola scriptura), that faith alone can lead to salvation (sola fide), that the Pope does not have universal jurisdiction over the whole Church, that the Catholic Church is not "the sole Church of Christ", and that there is no sacramental and ministerial priesthood received by ordination, but only a universal priesthood of all believers.[22]

In addition to these councils there have been a number of significant councils meant to further define the Eastern Orthodox position. They are the Synods of Constantinople in 1484, 1583, 1755, 1819, and 1872, the Synod of Iaşi (Jassy), 1642, and the Pan-Orthodox Synod of Jerusalem, 1672.

Within the Eastern Orthodox Church, the role of the ecumenical councils was to better define the Orthodox canon of faith, however the Eastern Orthodox Church authorities are not known to have authorized the use of violence in the persecution of heretics with nearly the frequency of their Western counterparts. Some individual examples of the execution of Orthodox heretics do exist, however, such as the execution of Avvakum in 1682. Far more typically, the Eastern Orthodox response to a heresy would rather be (and still is) to merely "excommunicate" the individuals involved.